With recent reduction in size of an electronic device, a demand for a high-capacity secondary battery is increasing. Particularly, a nonaqueous secondary battery having a higher energy density than a nickelcadmium battery or a nickelhydrogen battery is attracting attention.
As for a negative electrode active material of a nonaqueous secondary battery, graphite is often used in view of a cost, a durability and a capacity. However, when an active material layer comprising the negative electrode active material on an electrode is increased in a density for obtaining a high capacity, there arises a problem that a charge-discharge irreversible capacity at an initial cycle increases.
Patent Document 1 describes a production method of a carbon composite material, where natural graphite and a binder are kneaded to obtain a kneaded material, and the binder is carbonized by primary heating at 700 to 1,500° C., and subsequently secondary heating at 2,400 to 3,000° C. is performed, and then a purification of the natural graphite and a graphitization of the carbonized binder are simultaneously performed. However, in Patent Document 1, vein or flake natural graphite is envisaged as a starting material, and a increase in a density of an active material layer and a decrease in a charge-discharge irreversible capacity are insufficient.
Patent Document 1: JP-A-2000-086343 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)